The invention relates to a high-pressure discharge lamp comprising a discharge envelope enclosing a discharge space with a ceramic wall and provided with a pair of electrodes between which extends a discharge path. At least one electrode is provided with a rod which is connected to a tubular lead-through member and on which is arranged an emitter-containing element which is screened from the discharge space by means of a screening body. The expression "ceramic wall" is to be understood herein to mean a wall of monocrystalline oxide, such as, for example, sapphire, or of a polycrystalline oxide, such as for example, densely sintered aluminium oxide.
Such a lamp electrode is known from U.S. Pat. No. 3,911,313. In this case, the lead-through member and the screening body are made in one piece and the electrode rod is fixed by means of a restriction of the screening body with respect to the screening body by means of solder. At the area of the emitter-containing element, the screening body has a widened cross-section. The restriction further has for its object to position the emitter-containing element.
Further, structure is generally known in which the emitter-containing element is comprised of a first coil winding which is separated from the discharge space by a second coil winding at the area of the first coil winding (see, for example, U.S. Pat. No. 4,152,620).
In many types of high-pressure discharge lamps (the saturated vapor discharge lamp), one or more constituents of the filling of the discharge envelope are present in excess quantities. This results in the pressure of such a constituent during operation of the lamp being determined by the temperature at the area at which the filling constituent is present in excess quantity. The area at which the excess quantity of the relevant filling constituent is present in the so-called coldest spot or simply "cold spot" and is generally located near a lead-through member of the discharge envelope.
A general problem in such lamps is that due to an excessively low temperature of the coldest spot the pressure of the filling constituent present in excess quantity is lower than is desirable. The invention provides means by which this problem is avoided or at least mitigated. Another problem occurs when the coldest area is constituted in part by the lead-through member. In this case, there is a risk of the discharge directly applying to the excess filling.